The long term objective of the proposed study is to obtain a better understanding of blood coagulation mechanisms by identification of the molecular defects in four different human dysfibrinogens, and application of this information to the study of functional domains in normal human fibrinogen. Since these four dysfibrinogens exhibit different abnormal functional characteristics, the molecular defects will also be different. Thus, from four perspectives we have the opportunity to provide new knowledge regarding (a) functionally important domains in fibrinogen (b) mechanisms of fibrinopeptide release and fibrin monomer polymerization, (c) fibrinogen ultrastructure and (d) biologic activity of fibrinogen fragments. The specific aims of the proposed study are: (1) to completely characterize the functional defects of four dysfibrinogens; (2) to identify the molecular defects responsible for the abnormal coagulation behavior of four dysfibrinogens; (3) to use peptides containing the molecular defects as probes for study of coagulation mechanisms including fibrinopeptide release, fibrin monomer polymerization, calcium binding fibrin ligation, fibrinogen ultrastructure, and biological activity of fibrinogen fragments. The methodology required to accomplish these goals will include standard clinical assays and standard analytical techniques. A novel, systematic approach to the production, HPLC analysis, and isolation of protease-derived fibrinogen fragments has been developed and will be employed. The health relatedness of this proposal stems primarily from the possibility that fragments or peptides containing the molecular defect may exhibit anticoagulant activity. The information derived from studying the behavior of these altered molecular probes will ultimately have therapeutic applications. Moreover, the identification of loci in which single amino acid substitutions produce functional defects will elucidate the role that portion of the molecule plays in coagulation, produce a greater understanding of the structural domains in fibrinogen, and thereby permit a rational approach to treatment of fibrinogen-related coagulopathies.